High Degree Of Vacuum Research Articles

Deoxidation of Nickel-based Superalloy Using Carbon under High Vacuum Degree

Deoxidation of Nickel-based Superalloy Using Carbon under High Vacuum Degree

Vacuum-driven orientation of Nanostructured polystyrene-block-Poly(L-lactide) block copolymer thin films for Nanopatterning

Herein, we demonstrate a simple approach to control the orientation of cylinder-forming nanostructures in polystyrene-block-poly(L-lactide) (PS-b-PLLA) BCP thin films through thermal annealing under a high-vacuum environment. Surface tension discrepancy between the constituent blocks is critical in controlling the aimed orientation of self-assembled nanostructures in block copolymer (BCP) thin films. For BCP self-assembly, temperature has been widely utilized as a thermodynamic state variable under ambient pressure conditions, whereas the use of high vacuum (low pressure) for thermal annealing is limited. It has been observed that temperature can alter the surface tension only marginally with increasing temperature for polymeric materials; as a result, the pressure dependence of surface tension for PS and PLLA was investigated. By increasing the vacuum degree during thermal annealing, the surface tension discrepancy between the PS and PLLA blocks can be reduced significantly. Accordingly, during thermal annealing under high vacuum degree, a neutral air polymer interface can be generated for the BCP thin films, resulting in the formation of perpendicular cylinders from the neutral surface of the thin film through BCP microphase separation.

Characteristics of tin droplet target system for EUV source research

Droplet-based laser-produced plasma source shows enormous significance in extreme ultraviolet lithography, which places high demands on the stability of tin droplets. This paper presents a tin droplet target system including the tin droplet generator (DG), droplet diagnosis, and spatiotemporal synchronization of tin droplets and laser. Shadowgraph technology is used to determine the stability of tin droplets. The characteristics of the DG were analyzed, and the operation parameter maps are provided. By varying operating frequencies from 18.4 kHz to 49.3 kHz, the diameter and spacing of droplets can be adjusted in the ranges of 120–200 μm and 200–1100 μm respectively. Both theoretical calculations and experimental results show that tin droplets keep high stability when the operation parameters locate at the optimal range. The long-term lateral stability is also proven under a high degree of vacuum. Additionally, the application feasibility of the DG system is verified by the experiments of laser impact tin droplets.

Strategies for preventing gelation in preparation of hyperbranched benzoxazines with high performance

The gelation of linear oligomeric benzoxazine precursors (OBPs) and high-molecular-weight benzoxazine precursors (HMWBPs) have been noticed and addressed by various effective actions, while no similar reports on hyperbranched benzoxazoles have been available. A series of hyperbranched benzoxazines were synthesized by A2 + B3 method using 1,3-bis(3-aminopropyl)tetramethyldisiloxane (BATSi) and 1,1,1-tris(4-hydroxyphenyl)ethane (THPE) and paraformaldehyde, namely HB-TSis, to examine the conditions for preventing gelation. We found that in most cases, increasing the feeding molar ratio of -OH to NH2 group, prolonging the reaction time and increasing the reactant concentration were all favorable for the formation of soluble HB-TSis. Except when the molar ratio of -OH to NH2 was 2:3, a lower reactant concentration was more likely to avoid gel formation. A sufficiently high vacuum degree during drying was reported for the first time as a factor affecting the gelation of polybenzoxazine precursors. In addition, gelation-free HB-TSis exhibited high degrees of branching (DBs) and weight-average molecular weight (Mw) in the range of 0.58–0.69 and 6100–10,100 Da, respectively. Their cured resins, poly(HB-TSi)s, both perform well in terms of thermal stability with high char yield (Yc) varying from 37.9 to 56.2%, and flame retardancy with low the heat release capacity (HRC) varying from 49.9 to 81.9 J/(g K), which are capable of being applied as nonignitable materials.

Moisture diffusion modelling and effect of microwave vacuum drying on drying kinetics and quality of yam

Microwave vacuum drying (MVD) is a rapid drying method, which can achieve a good balance between drying rate and quality. In the present work, the effects of MVD processes on the quality, drying kinetics, and moisture diffusion of yam (Dioscorea opposita L.) were investigated. Results indicated that the loss of moisture in the MVD of yam slices mainly occurred in the stage with a constant and decreasing speed. When the moisture content of the dry base was decreased to about 1.3 g/g (dry basis, D.B.), it began to enter the deceleration phase. The effective moisture diffusivity (Deff) and mass transfer coefficient (km) increased following the power, loading amount at one time, and vacuum (pressure drop). The established equation of these parameters described well this variation law. Furthermore, a neural network model was established to predict the change in moisture content in the drying process, and the law of moisture diffusion was described. In terms of quality, the contribution ranked from high to low was loading, power, and pressure. Increasing the microwave power, loading, and maintaining a high vacuum degree could reduce energy consumption and ensure quality, thus improving the economic feasibility of microwave vacuum in the drying process.

Vacuum-Driven Orientation of Nanostructured Diblock Copolymer Thin Films.

This work aims to demonstrate a facile method for the controlled orientation of nanostructures of block copolymer (BCP) thin films. A simple diblock copolymer system, polystyrene-block-polydimethylsiloxane (PS-b-PDMS), is chosen to demonstrate vacuum-driven orientation for solving the notorious low-surface-energy problem of silicon-based BCP nanopatterning. By taking advantage of the pressure dependence of the surface tension of polymeric materials, a neutral air surface for the PS-b-PDMS thin film can be formed under a high vacuum degree (∼10-4 Pa), allowing the formation of the film-spanning perpendicular cylinders and lamellae upon thermal annealing. In contrast to perpendicular lamellae, a long-range lateral order for forming perpendicular cylinders can be efficiently achieved through the self-alignment mechanism for induced ordering from the top and bottom of the free-standing thin film.

50~500㎊ 커패시턴스 가변형 진공커패시터의 전극 설계 및 평가

A variable vacuum capacitor (VVC) is used to match impedance between an RF generator and a plasma load for manufacturing semiconductor devices and display panels. However, VVC requires a very narrow gap between electrodes and a high degree of vacuum to implement high dielectric strength and capacitance variability at compact sizes. In addition, it is difficult to manufacture and maintain quality of the electrode unit, and is not easy to access to development due to the difficulty of the brazing process. For this reason, there are no VVC manufacturers in Korea yet, so it relies entirely on imports.<BR>In this study, we designed and manufactured VVC with AC withstand voltage of 12 ㎸ and capacitance of 50 to 500 ㎊, which are widely used in RF matchers, etc. As a result of the test, the required performance was confirmed, and the possibility of localization was verified.

Influence of vacuum microwave drying parameters on the physicochemical properties of red beetroots

In recent years, the consumption of red beetroots has increased significantly due to its good taste, high nutritional value and abundant active compounds. Red beetroot is prone to spoilage due to its high moisture content, making it perishable. Vacuum microwave drying is a gentle drying method by inducing fast water evaporation from food products at low temperature, which can improves the product quality. The objective of this study was to investigate the effects of vacuum microwave drying parameters, including microwave power (500, 1000, and 1500 W) and vacuum degree (50, 70, and 90 KPa), on the physicochemical properties (drying time, rehydration ratio, color change, and contents of betalain and total phenolic) of red beetroots. The results showed that microwave power and vacuum degree had significant effects on the physicochemical properties of red beetroots. All the red beetroots after vacuum microwave drying had higher lightness (L*), lower redness (a*) and yellowness (b*) than that of fresh red beetroots. The drying time, rehydration ratio, betacyanin content and betaxanthin content of red beetroots decreased significantly with the increase of microwave power (P &lt; 0.05), while the rehydration ratio, color parameters (a*, b*, and chroma values), betacyanin content and betaxanthin content of red beetroots significantly increased with the increase of vacuum degree (P &lt; 0.05). Compared with other microwave powers, the red beetroots dried at 500 W showed longer drying time, higher rehydration ratio, more yellowish hue, and higher contents of betacyanin and betaxanthin. The lowest values of total color difference (∆E) and hue angle (H°) of dried red beetroots were obtained at microwave power of 1500 W. The dried red beetroots obtained at 90 KPa had the shortest drying time, the highest rehydration ratio, the best color, and the highest contents of betacyanin and betaxanthin. Meanwhile, the red beetroots dried at 50 KPa had the highest total phenolic content (12.47 ± 0.09 mg GAE/g). Based on the physicochemical properties of red beetroots, vacuum microwave drying at low microwave powers and high vacuum degree appears to be a suitable method for drying red beetroots.

Study on adaptive heat transfer performance of high temperature heat pipe

High temperature heat pipe (HTHP) employs alkali metal or its alloy as working fluid. Due to the large latent heat of its working fluid during phase change heat transfer, HTHP has the advantages of high temperature uniformity, high working temperature and high intensity heat transfer capacity, which has broad application prospects in the field of HTHP cooled nuclear reactors and the thermal protection of hypersonic vehicles. In order to simplify the structure of heat transfer system in nuclear reactors, so that it can safely and reliably realize passive heat transfer without additional pump power under various operating conditions, HTHP must have adaptive heat transfer capacity. In this paper, several HTHPs with excellent heat transfer performance are designed and prepared. The test-bed for frozen startup and heat transfer performance of HTHP is set up, and the electromagnetic induction high frequency heater is used as high temperature heat source. The thermal performance of HTHP with different heating power, heating position and the length of evaporation section (adaptive heat transfer characteristics) is experimentally studied, and the theoretical model is used to validate the experimental result. The experimental and theoretical results show that high vacuum degree is the prerequisite for excellent heat transfer performance of HTHP; high capillary driving force and suction force, reasonable filling ratio of working fluid are the key factors for HTHP to have adaptive heat transfer capacity, and the diameter of HTHP also has important influence on adaptive heat transfer capacity.

Design and construction of the Flux Core coils of the Space Plasma Environment Research Facility (SPERF)

A set of Flux Core coils are used to generate the model interplanetary magnetic field in the SPERF (Space Plasma Environment Research Facility) device to simulate the magnetic reconnection on the magnetopause of the earth. Several technical challenges are imposed on designing the coils in terms of electricity, vacuum, support, and motion, etc. The design and the construction of the Flux Core coils are presented in the paper to overcome the difficulties. Based on the structure parameters and the magnetic forces, the Flux Core coils composed of a G10 (fiberglass laminate composite material) form and several other components are designed. A complex construction process is used to acquire high vacuum degree and reliable insulation as well as fine surface quality. A support structure with a dedicated buffer mechanism is designed, with the ability to resist the magnetic forces according to a mass-spring-damper model and the mechanical analysis. The Flux Core coils are being built based on the design and the tests will be done later.

Moisture diffusion and shrinkage characteristics of broad bean during low-temperature vacuum drying

ABSTRACT Low-temperature vacuum dehydration could avoid heat injury because of high drying temperature, as well as prevent mechanical damage due to ice crystal during freezing. However, it is not clear for the effect of different temperatures and vacuum degrees on the dehydration process. The object of this work was to investigate the drying behavior of broad bean seed and to analyze the effect of moisture diffusion on the structure during low-temperature vacuum drying process. For this purpose, a test bench for low-temperature vacuum dehydration was designed and established. The nine dehydration operating conditions at temperatures of 0°C, 4°C, and 8°C and vacuum degrees of 95, 97, and 99 kPa were conducted. The key parameters including dehydration time, dehydration rate, shrinkage, effective moisture diffusivity were analyzed. Results showed that by increasing temperature and vacuum degree, the dehydration time obviously shortened, and the dehydration rate was significantly increased. The vacuum degree has an obvious influence on product shrinkage, especially in the thickness of broad bean seed. The average effective moisture diffusivity varied from 0.65 to 2.97 × 10−10 m2 s−1 under the tested drying conditions. And the high temperature and low vacuum degree were a better way for reducing the shrinkage of broad bean seed. To avoid structure collapse and cell rupture, the end moisture content of broad bean seed should be higher to 0.05 ~ 0.11.

The Research of Low-Oxygen Control and Oxygen Behavior during RH Process in Silicon-Deoxidization Bearing Steel

The variation of total oxygen (T.O) content, characterization of inclusions, slag composition, and off-gas behavior during the smelting process of silicon-deoxidization bearing steel were investigated with industrial experiments. The change of content of combined oxygen during RH (Ruhrstahl–Hereaeus vacuum degassing furnace) process was calculated and compared with T.O content change. It is found that the decrease of oxygen content is mainly caused by the removal of dissolved oxygen rather than the removal of oxides during RH process. Carbon was found to be a strong deoxidizer (stronger than aluminum) in high vacuum degree. Top slag is an oxygen source of the deoxidization process, leading to the re-oxidization of liquid steel, even though the FeO content is low in top slag. During the RH process, the change of oxygen mainly exists in three processes: 1) Deoxidization reaction in vacuum chamber, 2) oxygen mass transfer process between liquid steel out from a vacuum chamber and in ladle, and 3) oxygen mass transfer between ladle slag and liquid steel. It depends mainly on the mass transfer of the oxygen in the liquid steel.

Preparation method of low-oxygen Ti-6Al-4V alloy by solid state re-deoxidation using calcium

ABSTRACTThe oxygen concentration in commercial Ti-6Al-4 V alloys was reduced to less than 400 ppm in this study by the method of solid state re-deoxidation, using calcium as a reductant. The concentration of oxygen in the deoxidised Ti-6Al-4 V alloy was 630 ppm at the optimum deoxidation temperature of 1000°C. When the degree of vacuum was increased and re-deoxidation was carried out, the oxygen concentration decreased to 355 ppm. Therefore, it is possible to prepare a Ti-6Al-4 V alloy with an oxygen concentration of less than 400 ppm by using the solid state re-deoxidation method at a high degree of vacuum of 1.5 × 10-6 Torr.

Effect of vacuum degree on adhesion strength and corrosion resistance of magnetron sputtered aluminum coating on NdFeB magnet

A pure aluminum (Al) coating was deposited by direct current (DC) magnetron sputtering onto sintered NdFeB magnet coupons and glass slides at different vacuum degrees. The effect of vacuum degree on adhesion strength and corrosion resistance of the coating was investigated. The results showed that the adhesion strength between the Al coating and the substrate NdFeB magnet increased first and then decreased while the corrosion resistance of the Al coating increased with increasing vacuum degree. The Al coating formed at the low vacuum degree fractured within the coating when being peeled off because of a relatively high density of coating defects, while that formed at the high vacuum degree was mainly debonded along the coating/substrate interface. The decreased adhesion strength when the vacuum degree further increased could be attributed to excessive internal stress. The Al coating deposited at high vacuum degree was more corrosion resistant than that formed at low vacuum as the coating becomes less porous. Due to the presence of the micro defects, the corrosion behavior of the Al coating was accelerated on the substrate NdFeB magnet through the galvanic effect via these defects.

Interface characteristics and fracture behavior of hot rolled stainless steel clad plates with different vacuum degrees

In order to investigate the effect of vacuum degree on the interface microstructure and mechanical properties of stainless steel clad plate, series of 316L/Q235 clad plates were successfully fabricated by hot rolling with different vacuum degrees of 105 Pa, 400 Pa, 10 Pa, 10−1 Pa and 10−2 Pa. Interestingly, with the increase of vacuum degree, the interface oxides distribution changed from continuous wall/film to dispersed refined particles, and the thicknesses of martensite layer, decarburized layer and carburized layer were gradually increased. Meanwhile, the interface bonding strength of clad plates can be effectively enhanced by improving the vacuum degree. Due to thin decarburized and carburized layers, the stainless steel clad plate with a low vacuum degree of 105 Pa reveals superior yield strength and ultimate strength, while a low fracture elongation was obtained due to severe interface delamination. However, the stainless steel clad plate with a high vacuum degree can obtain a superior tensile ductility, which is attributed to the strong interface and localized necking delaying effect.

Experimental study on gas explosion suppression by coupling CO2 to a vacuum chamber

An experimental apparatus is set up to study the methane and air mixture explosion under the effect of vacuum chamber coupled with CO2. A series of experiments have been performed to analyze the effect of CO2/vacuum chamber on explosion strength and explosion suppression. The results show that: 1) When the vacuum degree is specified at 0.05 MPa, with the increase of CO2 concentration, the explosion suppression performance of the vacuum chamber increases gradually. Under the effect of the vacuum chamber, the higher the vacuum degree is, the more significant the suppression effect is. 2) Under the effect of the vacuum chamber/CO2, the optimum suppression effect is at lower vacuum degree coupled with CO2. 3) The optimum suppression effect of vacuum chamber/CO2 is with low vacuum degree, which is better than the vacuum chamber in high degree without CO2. Therefore, coupling CO2 to vacuum chamber can improve the suppression performance of the vacuum chamber and lower the cost for maintaining a high vacuum degree. The investigation results can be used as a reference for the further research of vacuum chamber.

Statistical experimental study for verifying thermal characteristics of insulated double pipe

This study investigates the heat transfer characteristics of an insulated double pipe in accordance with the degree of vacuum and the working fluid pressure for liquefied natural gas transportation. A total of 16 cases were examined, and the degree of vacuum was set at 760, 0.1, 0.01 and 0.001 torr. Meanwhile, the working fluid pressure was set at 1, 3, 5 and 7 bar to analyze the effect of variables. A correlation analysis based on statistics was performed to quantitatively study the temperature distribution and the heat transfer characteristics. An approximated formula on the quantity of heat depending on the thermal conductivity of rarefied gas was also calculated. The approximated curve was compared with the theory formula. Consequently, the heat insulation property was improved in proportion to the degree of vacuum. A comparison of the approximated curve and the theory formula further showed that thermal conductivity was dominant at a high degree of vacuum.

Effects of osmotic dehydration vacuum-microwave drying on the properties of tilapia fillets

A novel drying method based on vacuum-microwave dehydration was developed to investigate the effects of different microwave gap ratios (MGR), microwave times, power densities and degrees of vacuum after osmotic pre-treatment on tilapia fillets. The results showed that the moisture value of fillets was decreased with the increased drying time, power density and vacuum degree. The shrinkage ratio, rehydration ratio and total colour change increased with elevated microwave time and power density. A high degree of vacuum was beneficial to the qualities of fillets. In conclusion, tilapia fillets retained their original quality properties after osmotically dehydrated vacuum-microwave drying (OD-VMD); optimum process parameters were MGR = 2, microwave time = 10 min, power density = 20 W/g, and vacuum degree = 0.08 MPa.

Effects of vacuum chopping on physicochemical and gelation properties of myofibrillar proteins from silver carp (Hypophthalmichthys molitrix)

Physicochemical and gelation properties of myofibrillar proteins from silver carp surimi as affected by chopping under different vacuum degrees (0, 0.01, 0.02, 0.04, 0.06 and 0.08 MPa) were investigated. With the increase of vacuum degree, size and quantity of air bubbles in surimi paste decreased, disulfide bond content of myofibrillar proteins decreased significantly (p < .05) and then slight increased (p > .05), while surface hydrophobicity of myofibrillar proteins increased gradually (p < .05). Gel mechanical properties, chemical interactions (nonspecific associations, hydrogen bond and hydrophobic interactions) and FAXL (cross-linking degree of free amino group) of heat-induced surimi gel increased significantly (p < .05) with vacuum degree. Scanning electron microscopy (SEM) observation showed that three-dimensional network of surimi gel under higher vacuum degree was more compact and orderly. Results indicated that vacuum chopping imparted physicochemical and structural changes of fish myofibrillar protein, which might contribute to the improvement in gelling properties of myofibrillar proteins.

The influence of different vacuum degree on the porosity and mechanical properties of aluminum die casting

AlSi9Cu3 alloy castings were produced by the vacuum-assisted high pressure die casting (HPDC) process under three different absolute pressures: 500 mbar, 200 mbar and 100 mbar. The influence of absolute pressure in the die cavity on the porosity, microstructure and mechanical properties of die castings were investigated. It shows that as the absolute pressure decreases, the average porosity and pore sizes reduce from 4.8% to 2.8%, 8.65 μm–5.61 μm respectively, and the tensile strength and elongation is improved markedly by 13%, 25.2% respectively. The specimens contain larger pores under higher absolute pressure. Meanwhile, it discovers that the shape of pores is also an important factor affecting the mechanical properties. The pores with sharp corner present are much more in the castings as the absolute pressure increases. As a whole, high vacuum degree contributes to reduce the porosity that would be the basis for subsequent heat treatment and improve mechanical properties.